Use WeakMap if available to avoid O(n) lookup

[sheerun]

Supersedes #57

[gaearon]

Do you want to extract this to an npm module? Inspired by your previous PR I implemented something similar here because I need it in that project too. Ideally I’d prefer this be an external module I could depend on in both projects.

[sheerun]

Isn't https://github.com/medikoo/es6-weak-map exactly what you're looking for?

[sheerun]

var WeakMap;

if (useWeakMap) {
  WeakMap = require('es6-weak-map');
} else {
  WeakMap = require('es6-weak-map/polyfill');
}

[gaearon]

I don’t really care that much about real WeakMap semantics—it’s fine to leak memory in older browsers in development mode during hot reloading. The problem with polyfills is they sometimes have tricky edge cases or may cause weird problems in some environments. Ideally I want to:

• Have full control over this code and understand it well.
• Don’t let it bring in 10 other ES6 polyfills.
• Use WeakMap when possible but otherwise I’m fine leaking memory.
• Not define any fields on the components. This is how any true WeakMap polyfill works, but in my case I’d rather avoid it to avoid issues like this. Proxies are already invasive, and putting fields on components forces us to think about weird edge cases, which I’d rather avoid.

[sheerun]

Do you wish to restrict input values to only objects? (just like WeakMap)

[gaearon]

Yeah, so that WeakMap case works.

[sheerun]

I think https://github.com/WebReflection/es6-collections implementation should suit you except:

1. It overrides global WeakMap
2. It also implements few other collections

I could fix both and extract code to the new module. OK?

[gaearon]

I’d really prefer my implementation in this case. The surface area I need is very small, and putting components into “slots” by their displayName/name reduces the lookup time for the common case. I think we can benefit from having a very specific use case (map by component) here.

[sheerun]

OK, I think I have full picture. I'll try to come up with something soon.

[wkwiatek]

Have you come up with something new? Or should we just close this?

[sheerun]

@wkwiatek Thanks for reminding.. I've created https://github.com/sheerun/component-map and update this PR to use it. ComponentMap includes lots of tests that also verify proper garbage collection. Hope you like it.

[sheerun]

@gaearon You might want to consider using component-map it in react-hot-loader as well